Hermetic screw compressor

ABSTRACT

A hermetic screw compressor comprises a male rotor, a female rotor engaging the male rotor, an electric motor connected to a low pressure side shaft portion of the male rotor, a low pressure side bearing for supporting the low pressure side shaft portion of each of the rotors, a high pressure side bearing for supporting a high pressure side shaft portion of each of the rotors, and a casing containing the rotors, the electric motors and the bearings. A contact type seal is arranged to seal a part of the low pressure side shaft portion of the male rotor between the low pressure side bearing and the electric motor, and a cover contains the seal and is axially detachably attached to the casing so that the contact type seal is attached to the casing through the cover.

BACKGROUND OF THE INVENTION

The present invention relates to a hermetic screw compressor to be used in an air conditioner or refrigerator.

A hermetic screw compressor has a screw rotor, a low-pressure side bearing for supporting the screw rotor, an electric motor for driving the screw rotor and a casing containing these elements. The electric motor may be arranged at either of low-pressure side and high-pressure side, but in many cases, is arranged at the low pressure side because the electric motor of high temperature is cooled at the low pressure side by a refrigerant gas of low-temperature and low pressure.

Further, a lubricating oil is generally supplied to a bearing by a difference in pressure between the low pressure side and the high-pressure side in the screw compressor. Since the oil of high-temperature and high-pressure is supplied to the bearing for supporting the screw rotor from an environment of the discharged gas, the oil flowing to the electric motor at the low-pressure side after lubricating the bearing of the low-pressure side heats an electrically insulating member of the electric motor to be deteriorated. Further, there is a problem of that the oil of high-temperature flowing out therefrom is mixed the refrigerant gas of low-temperature and low-pressure to be taken into tooth spaces of the screw rotor so that the refrigerant gas of low-temperature is heated by the oil to deteriorate a performance of the compressor.

Therefore, JP-A-2-275086 (FIG. 5) discloses a non-contact seal between the electric motor and the bearing of the low-pressure side for preventing the oil from flowing from the bearing of the low-pressure side to the low pressure side (the motor side).

BRIEF SUMMARY OF THE INVENTION

In JP-A-2-275086, a non-contact seal is used to obtain a sealing utilizing a frictional resistance of viscous liquid and a labyrinth effect, so its sealing performance is not sufficient for preventing the oil from flowing out.

Further, it is difficult for a non-contact seal for improving the oil sealing to be used, because it needs a maintenance operation for an abrasion of the seal or a shaft progressing in accordance with an increase of operating time period of the compressor.

An object of the present invention is to provide a hermetic screw compressor in which an oil of high temperature is prevented from flowing from a bearing of low-pressure side to a low-pressure side (motor side) and a maintenance is easy.

A first distinctive feature of the invention for achieving the object is that in a hermetic screw compressor comprising screw rotors each of which includes a teeth portion, a low pressure side shaft portion and a high pressure side shaft portion, an electric motor connected to the low pressure side shaft portion of at least one of the screw rotors, a low pressure side bearing for supporting the low pressure side shaft portion, a high pressure side bearing for supporting the high pressure side shaft portion, and a casing containing hermetically these elements, a contact type seal is arranged to seal a part of the screw rotor between the electric motor and the low pressure side bearing at the low pressure side shaft portion, and a cover contains the contact type seal and is detachably attached to the casing so that the contact type seal is attached to the casing through the cover.

In this case, it is preferable that a sleeve forms the part of the screw rotor with which the contact type seal contacts, and a hardness of the sleeve is higher than a hardness of the low pressure side shaft portion.

Incidentally, the screw rotors may include a pair of male and female rotors engaging each other, or a pair of screw rotor and gate roller engaging each other.

A second distinctive feature of the invention for achieving the object is that in a hermetic screw compressor comprising a screw rotor including a teeth portion of screw shape, and a rotor shaft monolithic with the teeth portion, an electric motor connected to the rotor shaft to be rotationally driven, a low pressure side bearing for supporting an intake side of the rotor shaft, a high pressure side bearing for supporting an exit side of the rotor shaft, and a casing containing these elements, the compressor further comprises a contact type seal arranged to seal the rotor shaft between the low pressure side bearing and the electric motor, and a bearing holder for holding the low pressure side bearing axially with respect to the casing, and the bearing holder contains the contact type seal so that the contact type seal is attached to the casing through the bearing holder.

In this case, it is preferable that the rotor shaft has a sleeve on which the contact type seal slides, and a hardness of the sleeve is higher than a remainder part of the rotor shaft.

A third distinctive feature of the invention for achieving the object is that in a hermetic screw compressor comprising a male rotor, a female rotor engaging the male rotor, an electric motor connected to a low pressure side shaft portion of the male rotor, a low pressure side bearing for supporting the low pressure side shaft portion of each of the rotors, a high pressure side bearing for supporting a high pressure side shaft portion of each of the rotors, and a casing containing these elements, a contact type seal is arranged to seal a part of the low pressure side shaft portion of the male rotor between the low pressure side bearing and the electric motor, a cover contains the seal and axially detachably attached to the casing so that the contact type seal is attached to the casing through the cover, the low pressure side shaft portion has a sleeve arranged to slide with respect to the contact type seal, and a hardness of the sleeve is higher than a hardness of a remainder part of the low pressure side shaft portion.

In this case, the low pressure side shaft portion and the high pressure side shaft portion may be monolithically included by each of the rotors, while the low pressure side shaft portion of the male rotor may be directly connected to the electric motor to be rotationally driven.

The contact type seal may be an oil seal or a mechanical seal.

According to the invention, since a contact type seal is arranged to seal a part of the screw rotor between the electric motor and the low pressure side bearing at the low pressure side shaft portion, and a cover contains the contact type seal and is detachably attached to the casing so that the contact type seal is attached to the casing through the cover, a hermetic screw compressor of high performance and high reliability in which an oil of high temperature and high pressure is prevented from flowing to the low pressure side, and an ease of maintenance is improved, is obtainable.

When a contact type seal is arranged between the electric motor and the low pressure side bearing to prevent the oil from flowing from the low pressure side bearing to the low pressure side (motor side), the sealing performance is significantly improved, but a maintenance is necessary, because the seal or the shaft to be seal is worn away in accordance with an increase of compressor operating time period. According to the invention, the contact type seal is arranged in the screw compressor while the contact type seal is detachably attached, so that the hermetic screw compressor of high performance and high reliability with improved ease of maintenance is obtainable.

Hereafter, embodiments of the invention will be described with making reference to the drawings.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a longitudinally cross sectional view showing an embodiment of the invention.

FIG. 2 is an enlarged partially cross sectional view showing a low-pressure side in the vicinity of a bearing.

FIG. 3 is an enlarged partially cross sectional view showing a low-pressure side in the vicinity of a bearing in a second embodiment of the invention.

FIG. 4 is an enlarged partially cross sectional view showing a low-pressure side in the vicinity of a bearing in a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross sectional view showing a hermetic screw compressor as an embodiment of the invention. Although a hermetic twin-screw compressor of the invention will be described below, the invention is not applicable only to the twin-screw type, but also to a single-screw type including a screw rotor and a gate rotor engaging each other.

A hermetic screw compressor has a motor casing 1, a main casing 2 and an discharge casing 3 hermetically connected to each other. The motor casing 1 contains a driving motor 4 for driving a compressing mechanism. The main casing 4 has cylindrical bores 5 and 6, and intake ports 7 and 8 for introducing a refrigerant gas into the cylindrical bores 5 and 6. The cylindrical bores 5 and 6 contains male and female rotors 16 and 17 engaging each other and supported by roller bearings 9, 10, 11, 12 and 13 and ball bearings 14 and 15, and the male rotor 16 is directly connected to the driving motor 4 at a low-pressure side. The main casing 2 has an oil separator 18 and an oil tank integrally formed with each other.

The discharge casing 3 containing the roller bearings 11 and 13 and the ball bearings 14 and 15 includes a discharge path (not shown) for the refrigerant gas communicating with the oil separator 18 of the main casing 2, and the discharge casing 3 is fixed to the main casing 2 by bolts or the like. Further, a shield plate 22 is attached to an end of the discharge casing 3 to cover bearing chambers 20 and 21 containing the roller bearings 11 and 13 and the ball bearings 14 and 15.

The main casing 2 and the discharge casing 3 include lubricating passages for making communications between the oil tank 19 of the main casing and the bearings.

Next, a flow of each of the refrigerant gas and the oil is described.

The refrigerant gas of low-temperature and low-pressure flowing from an inlet port 29 of the motor casing 1 passes a strainer 30 for collecting contaminant, and subsequently passes a gas passage between the driving motor 4 and the motor casing 1 and an air-gap between a stator 4a and a motor rotor 4b to cool the driving motor 4. The refrigerant gas is taken from the inlet port 7 and 8 of the main casing 2 into a compression chamber formed by the main casing 2 and teeth surfaces of the male and female screw rotors engaging each other after cooling the motor. Subsequently, the refrigerant gas is hermetically contained by the compressing chamber formed by the main casing 2 and teeth surfaces of the male and female screw rotors engaging each other in accordance with a rotation of the male rotor 16 connected to the driving motor 4 so that the refrigerant gas compressed by decrease in volume of the compressing chamber becomes of high-temperature and high-pressure to be discharged through a discharge passage (not shown) in the discharge casing into the oil separator 18 formed monolithically with the main casing 2. During the compression, a radial part of a compression reaction force applied to the male and female rotors is borne by the roller bearings 9, 10, 11, 12 and 13, and a thrust part thereof is borne by the ball bearings 14 and 15. The oil for lubricating and cooling these bearings flows from the oil tank 19 at the high-pressure area of the main casing 2 through the lubricating passages for these bearings with the differential pressure to be discharged with the refrigerant gas into the oil separator 18. The oil is separated from the compressed refrigerant gas in the oil separator 18 to be stored in the oil tank 19 monolithically formed with the main casing 2. The compressed refrigerant gas separated from the oil is discharged from the discharge port of the main casing 2.

FIG. 2 is an enlarged partial view showing the vicinity of the bearings 9, 10 and 12 at the low-pressure side as shown in FIG. 1. The oil supplied from the oil tank 19 at the high-pressure side passes through the lubricating passage 23 a the roller bearings 11 and 13 and the ball bearings 14 and 15 at the high-pressure side to be lubricated. On the other hand, a part of the oil passing the lubricating passage 23 b is supplied to the roller bearing 12 arranged at the low-pressure side to support the female rotor 17, and the remainder part thereof passing the lubricating passages 23 c and 23 d is supplied to the roller bearings 9 and 10 arranged at the low-pressure side to support the male rotor 16.

In the embodiment, a contact type seal 24 is arranged between the roller bearings 9 and 10 and the driving motor 4. In this case, the contact type seal 24 is an oil-seal. Further, the contact type seal 24 is contained by a bearing cover 25 mounted on the main casing 2. Therefore, the oil of high-temperature and high pressure is prevented from flowing to the low-pressure side so that the electrically insulating member of the driving motor 4 and the refrigerant gas of low-pressure and low-temperature are prevented from being heated excessively by the oil to obtain high performance and reliability. Further, since the contact type seal 24 is contained by the bearing cover 24 to be detachably mounted, the maintenance of the contact type seal 24 is easily done by detaching the bearing cover 25 when the abrasion of sealing region of the contact type seal 24 progresses in accordance with an increase of operating time period of the compressor.

Embodiment 2

FIG. 3 shows a second embodiment and corresponds to FIG. 2.

In this embodiment, a sleeve 26 is fitted on a shaft portion 27 at the low-pressure side of the male rotor 16. When the contact type seal 24 is the oil seal whose material is rubber or plastic, a material of the shaft for the seal is steel or casting iron so that the seal is worn away in accordance with the increase of the compressor operating time period. On the contrary, when a contaminant such as iron powder or the like exists on the sealing area, the shaft is worn away so that the male rotor 16 should be exchanged for the maintenance to increase the cost therefore. In this embodiment, the sleeve 26 is fitted on the shaft portion 27 of the low-pressure side and a hardness of the sleeve 26 is higher than that of the shaft portion 27 to restrain the abrasion of the sleeve 26 so that it is difficult for the sleeve 26 to be worn away and the sleeve 26 is exchangeable to improve an ease of maintenance and to decrease the cost of maintenance when the sleeve is worn away.

Embodiment 3

FIG. 4 shows a third embodiment and corresponds to FIG. 2.

In this embodiment, the contact type seal is a mechanical seal 28. The mechanical seal 28 has a complex structure in comparison with the oil seal, but brings about an improved sealing performance so that a provability of that the oil of high pressure and high temperature flows to the low pressure side is decreased significantly to obtain the hermetic screw compressor of improved performance and reliability.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A hermetic screw compressor comprising, screw rotors each of which includes a teeth portion, a low pressure side shaft portion and a high pressure side shaft portion, an electric motor connected to the low pressure side shaft portion of at least one of the screw rotors, a low pressure side bearing for supporting the low pressure side shaft portion, a high pressure side bearing for supporting the high pressure side shaft portion, and a casing containing hermetically the screw rotors, the electric motor, the low pressure side bearing and the high pressure side bearing, wherein the compressor further comprises a contact type seal arranged to seal a part of the screw rotor between the electric motor and the low pressure side bearing at the low pressure side shaft portion, and a cover containing the contact type seal and detachably attached to the casing.
 2. The hermetic screw compressor according to claim 1, wherein the screw rotor has a sleeve forming the part of the screw rotor with which the contact type seal contacts, and a hardness of the sleeve is higher than a hardness of the low pressure side shaft portion.
 3. The hermetic screw compressor according to claim 1, wherein the screw rotors includes a pair of male and female rotors engaging each other.
 4. The hermetic screw compressor according to claim 1, wherein the screw rotors includes a pair of screw rotor and gate roller engaging each other.
 5. A hermetic screw compressor comprising, a screw rotor including a teeth portion of screw shape, and a rotor shaft monolithic with the teeth portion, an electric motor connected to the rotor shaft to be rotationally driven, a low pressure side bearing for supporting an intake side of the rotor shaft, a high pressure side bearing for supporting an exit side of the rotor shaft, and a casing containing the screw rotor, the electric motor, the low pressure side bearing and the high pressure side bearing, wherein the compressor further comprises a contact type seal arranged to seal the rotor shaft between the low pressure side bearing and the electric motor, and a bearing holder for holding the low pressure side bearing axially with respect to the casing, the bearing holder containing the contact type seal so that the contact type seal is attached to the casing through the bearing holder.
 6. The hermetic screw compressor according to claim 5, wherein the rotor shaft has a sleeve on which the contact type seal slides, and a hardness of the sleeve is higher than a remainder part of the rotor shaft.
 7. A hermetic screw compressor comprising, a male rotor, a female rotor engaging the male rotor, an electric motor connected to a low pressure side shaft portion of the male rotor, a low pressure side bearing for supporting the low pressure side shaft portion of each of the rotors, a high pressure side bearing for supporting a high pressure side shaft portion of each of the rotors, and a casing containing the rotors, the electric motors and the bearings, wherein the compressor further comprises a contact type seal arranged to seal a part of the low pressure side shaft portion of the male rotor between the low pressure side bearing and the electric motor, and a cover containing the seal and axially detachably attached to the casing so that the contact type seal is attached to the casing through the cover, the low pressure side shaft portion has a sleeve arranged to slide with respect to the contact type seal, and a hardness of the sleeve is higher than a hardness of a remainder part of the low pressure side shaft portion.
 8. The hermetic screw compressor according to claim 7, wherein the low pressure side shaft portion and the high pressure side shaft portion are monolithically included by each of the rotors, and the low pressure side shaft portion of the male rotor is directly connected to the electric motor to be rotationally driven.
 9. The hermetic screw compressor according to claim 1, wherein the contact type seal is an oil seal.
 10. The hermetic screw compressor according to claim 1, wherein the contact type seal is a mechanical seal. 